This invention relates to a rubber composition for the treads of high-performance tires including racing tires. In the rubber composition the essential elastomer component is a blend of a conventional diene rubber such as styrene-butadiene rubber and a low molecular weight copolymer of an aliphatic diene and an aromatic vinyl compound.
For the treads of racing tires, it is known to use a rubber composition containing a large amount of a softening agent represented by aromatic oil with a view to enhancing the road gripping ability. Certainly, the inclusion of a large amount of aromatic oil or an equivalent is effective in increasing the hysteresis loss value (tan .delta.). However, from broad considerations this measure has proved to be unfavorable because some important characteristics of tire treads such as rupture strength, wear resistance and blowout resistance are significantly marred by the increased softening agent.
An example of conventional rubbers used in the treads of racing tires in view of high hysteresis loss values is high-styrene styrene-butadiene copolymer rubber prepared by emulsion polymerization. However, this rubber is rather inferior in vulcanizability together with anotier diene rubber and is not sufficiently high in rupture strength. U.S. patent application Ser. No. 755,997 filed July 17, 1985, now abandoned, in which the joint inventors include the both inventors of the present application, discloses a tire tread rubber composition comprising a copolymer of an aliphatic diene and an aromatic vinyl compound prepared by solution polymerization.